Adaptive optics apparatus, adaptive optics method, and imaging apparatus

ABSTRACT

An adaptive optics apparatus includes an aberration measuring unit that measures an aberration caused by a subject&#39;s eye, the aberration being measured on the basis of returning light that returns from the subject&#39;s eye; an aberration correcting unit that performs aberration correction in accordance with the aberration measured by the aberration measuring unit; an irradiation unit that irradiates the subject&#39;s eye with light corrected by the aberration correcting unit; and an adjusting unit that maintains a correction characteristic of the aberration correcting unit when the subject&#39;s eye moves out of a predetermined area.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical imaging method using anadaptive optics system and an optical imaging apparatus including theadaptive optics system. More particularly, the present invention relatesto a method for obtaining a fundus image in which an aberration of asubject's eye is measured and corrected.

2. Description of the Related Art

Recently, scanning laser ophthalmoscopes (SLO) which two-dimensionallyirradiate a fundus with a laser beam and receive light reflected by thefundus and imaging apparatuses using interference of low-coherence lighthave been developed as ophthalmologic imaging apparatuses.

The imaging apparatuses using the interference of low-coherence light iscalled optical coherence tomography (OCT) apparatuses, and is used, inparticular, to obtain a tomographic image of a fundus or an area aroundthe fundus.

Various types of OCT, such as time domain OCT (TD-OCT) and spectraldomain OCT (SD-OCT), have been developed.

In the ophthalmologic imaging apparatuses, recently, the numericalaperture (NA) of the laser has been increased, and the resolution hasbeen increased accordingly.

However, in the process of obtaining an image of a fundus, the fundus isirradiated with a laser beam through optical tissues, such as a corneaand a lens, of an eye.

As the resolution increases, the influence of an aberration of thecornea and the lens on the quality of the obtained image increases.

Accordingly, researches on adaptive optics SLO (AO-SLO) and adaptiveoptics OCT (AO-OCT) have been conducted. In AO-SLO and AO-OCT, anadaptive optics (AO) system, which is an adaptive optics system formeasuring and correcting an aberration of the eye, is adopted. Anexample of AO-OCT is described in Optics Express, Vol. 14, No. 10, 15May 2006, by Y. Zhang et al. In AO-SLO and AO-OCT, a wavefront of an eyeis generally measured by a Shack-Hartmann wavefront sensor method.

In the Shack-Hartmann wavefront sensor method, the wavefront is measuredby causing measurement light to be incident on the eye and receivinglight reflected by the eye with a CCD camera through a microlens array.In AO-SLO and AO-OCT, a high-resolution image can be obtained by drivingcomponents such as a deformable mirror and a spatial phase modulator soas to correct the measured wavefront and obtaining an image of a fundusthrough the components. In an imaging apparatus including theabove-described adaptive optics system according to the related art,feedback control is performed by repeating a process of measuring theaberration of the eye for correcting the aberration and a correctingprocess based on the measured aberrations.

The feedback control is performed to compensate for an error between acommand value supplied to a correction device and an actual amount ofcorrection and a variation in aberration caused in accordance with thestate of lacrimal fluid and the state of refraction adjustment of theeye.

Similar to general feedback control, in the aberration correctioncontrol, it takes a certain time to establish a state in which theaberration is appropriately corrected after the control operation isstarted.

In particular, since response speeds of the wavefront sensor and awavefront correction device used to correct the aberration are low, ittakes several seconds to several tens of seconds to establish the statein which the aberration is appropriately corrected.

SUMMARY OF THE INVENTION

In an optical tomographic imaging apparatus, such as an OCT apparatus,that obtains an image of a fundus, it takes a relatively long time tocomplete an operation of obtaining an image of an eye after theoperation is started. Therefore, there is a high possibility that theeye will temporarily move horizontally or vertically during the imagingoperation.

In the case where the eye moves, it is useless to obtain an image of theeye since the imaging position is displaced from a desired position.Therefore, the imaging operation is resumed after the eye returns to theoriginal position.

When the eye moves, a light path along which measurement light travelschanges, and the measured aberration largely varies as a result.

Accordingly, in the aberration correction based on the above-describedfeedback control, the feedback control is performed so as to correct theaberration that has been varied, and the correction state changes fromthe original correction state.

Therefore, according to the related art, when the eye returns to thedesired position, the time required to establish the state in which theaberration is appropriately corrected increases. Thus, it is difficultto quickly obtain an image of the fundus.

In light of the above-described situation, the present inventionprovides an optical imaging method using an adaptive optics system andan optical imaging apparatus including the adaptive optics system, theadaptive optics system being capable of reducing the time of feedbackcontrol required to appropriately correct an aberration when theposition of a test object, which is an object of which an image is to beobtained, is moved. The present invention provides an optical imagingmethod using an adaptive optics system and an optical imaging apparatusincluding the adaptive optics system having the following structure.

An adaptive optics apparatus according to an aspect of the presentinvention includes an aberration measuring unit that measures anaberration caused by a subject's eye, the aberration being measured onthe basis of returning light that returns from the subject's eye; anaberration correcting unit that performs aberration correction inaccordance with the aberration measured by the aberration measuringunit; an irradiation unit that irradiates the subject's eye with lightcorrected by the aberration correcting unit; and an adjusting unit thatmaintains a correction characteristic of the aberration correcting unitwhen the subject's eye moves out of a predetermined area.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings. Further features of the present invention will becomeapparent from the following description of exemplary embodiments withreference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating the structure of an opticalimaging apparatus including an SLO provided with an adaptive opticssystem according to a first embodiment of the present invention.

FIG. 2 is a schematic diagram illustrating the structure of an opticalimaging apparatus including an OCT apparatus provided with an adaptiveoptics system according to a second embodiment of the present invention.

FIG. 3A is a schematic diagram illustrating a deformable mirror as anexample of a wavefront correction device according to the firstembodiment of the present invention.

FIG. 3B is a schematic diagram illustrating a reflective liquid-crystallight modulator as another example of the wavefront correction deviceaccording to the first embodiment of the present invention.

FIGS. 3C and 3D are schematic diagrams illustrating the structure of aShack-Hartmann sensor as an example of a wavefront sensor according tothe first embodiment of the present invention.

FIG. 3E is a schematic diagram illustrating the state in a light ray ofwhich a wavefront is measured is collected on a CCD sensor according tothe first embodiment of the present invention.

FIGS. 3F and 3G are schematic diagrams illustrating a case in which awavefront having a spherical aberration is measured according to thefirst embodiment of the present invention.

FIGS. 4A to 4C are graphs illustrating an aberration correction functionprovided by the adaptive optics system according to the first embodimentof the present invention.

FIG. 5 is a flowchart illustrating an example of control steps accordingto the first embodiment of the present invention.

FIG. 6 is a flowchart illustrating another example of control stepsaccording to the first embodiment of the present invention.

FIG. 7 is a schematic diagram illustrating the structure of an opticalimaging apparatus, which is an SLO, including an adaptive optics systemaccording to a third embodiment of the present invention.

DESCRIPTION OF THE EMBODIMENTS

Embodiments of the present invention will now be described. However, thepresent invention is not limited to the structures of the embodimentsdescribed below.

First Embodiment

An optical imaging apparatus and an optical imaging method in which anoptical image of a test object is obtained by an SLO including anadaptive optics system according to a first embodiment of the presentinvention will be described with reference to FIG. 1.

According to the present embodiment, the test object, which is ameasurement object, is an eye, and an image of a fundus of the eye isobtained by the optical imaging apparatus, which is the SLO, includingthe adaptive optics system. An eyepiece section of this apparatus issimilar to that in an optical coherence tomography (OCT) apparatus.

Referring to FIG. 1, in the present embodiment, a light source 101 is asuperluminescent diode (SLD) with a wavelength of 840 nm.

The wavelength of the light source 101 is not particularly limited.However, in an apparatus for obtaining an image of a fundus, thewavelength can be set in the range of 800 nm to 1,500 nm to reduce glarefor a subject and maintain the resolution.

Although the SLD is used in the present embodiment, a laser, forexample, may instead be used.

In the case where the laser is used, a structure for reducing coherence,such as a long optical fiber, may be additionally used to reduce specklenoise.

In the present embodiment, a common light source is used for bothobtaining the image of the fundus and measuring a wavefront. However,separate light sources may be used, and light rays from the respectivelight sources may be combined together at an intermediate position.

Light emitted from the light source 101 travels through a single-modeoptical fiber 102, is collimated by a collimator 103, and is emitted ascollimated light.

Measurement light 105 emitted from the collimator 103 passes through abeam splitter 104, which is a light splitting unit, and is guided to anadaptive optics system.

The adaptive optics system includes a beam splitter 106, which is alight splitting unit, a wavefront sensor (aberration measuring unit)115, a wavefront correction device (aberration correcting unit) 108, andreflection mirrors 107-1 to 107-4.

The reflection mirrors 107-1 to 107-4 are arranged such that at leastthe pupil of the eye is optically conjugate with the wavefront sensor115 and the wavefront correction device 108.

In the present embodiment, a deformable mirror is used as the wavefrontcorrection device 108.

The deformable mirror is capable of locally changing a light reflectiondirection thereof. Various types of deformable mirrors are in practicaluse.

For example, a device illustrated in FIG. 3A may be used as thewavefront correction device 108.

The device illustrated in FIG. 3A includes a film-shaped deformablemirror surface 127 that reflects incident light, a base portion 126, andactuators 128 disposed between the mirror surface 127 and the baseportion 126.

With regard to the principle of operation of the actuators 128, theactuators 128 may be operated using electrostatic force, magnetic force,piezoelectric effect, etc., and the structure of the actuators 128differs depending on the principle of operation thereof.

The actuators 128 are two-dimensionally arranged on the base portion126, and are selectively driven so that the shape of the mirror surface127 can be changed.

A spatial phase modulator (reflective liquid-crystal light modulator)including a liquid crystal element illustrated in FIG. 3B is anotherexample of the wavefront correction device 108.

This spatial phase modulator is structured such that liquid crystalmolecules 132-1 and 132-2 are enclosed in a space surrounded by a baseportion 129 and a cover 130.

A plurality of pixel electrodes 131 are provided on the base portion129, and a transparent counter electrode (not shown) is provided on thecover 130.

When no voltage is applied between the electrodes, the liquid crystalmolecules are oriented similarly to the liquid crystal molecules denotedby 132-1. When a voltage is applied, the liquid crystal molecules areoriented similarly to the liquid crystal molecules denoted by 132-2.Accordingly, the refractive index of the incident light changes inaccordance with the orientation of the liquid crystal molecules.

The phase can be spatially modulated by changing the refractive index ateach of the pixels by controlling the voltage applied to each of thepixel electrodes 131.

For example, in the case where light 133 is incident on the element, thephase of a light component that passes through the liquid crystalmolecules 132-2 is delayed with respect to the phase of a lightcomponent that passes through the liquid crystal molecules 132-1. As aresult, a wavefront 134 illustrated in FIG. 3B is formed.

Since the liquid crystal element has a polarization property, the liquidcrystal element is generally provided with a polarizing plate or thelike for adjusting the polarization of the incident light.

The light that has passed through the adaptive optics system isone-dimensionally or two-dimensionally scanned by a scanning opticalsystem 109.

In the present embodiment, the scanning optical system 109 includes twogalvano scanners for scanning the light in a main scanning direction(horizontal direction of the fundus) and a sub-scanning direction(vertical direction of the fundus). To achieve high-speed imagingoperation, a resonance scanner may instead be used in the scanningoptical system 109 for scanning the light in the main scanningdirection.

Depending on the structure of the scanning optical system 109, anoptical system including mirrors and lenses may be disposed between thescanners so as to set the scanners in the scanning optical system 109 toan optically conjugate state.

The measurement light scanned by the scanning optical system 109 isincident on an eye 111 through ocular lenses 110-1 and 110-2.

The measurement light incident on the eye 111 is reflected and diffusedby the fundus.

The eye 111 can be appropriately irradiated with the measurement lightin accordance with the visibility thereof by adjusting the positions ofthe ocular lenses 110-1 and 110-2.

Although lenses are included in the eyepiece section in the presentembodiment, spherical mirrors or the like may be used instead.

The light reflected and diffused by a retina of the eye 111 travels inthe reverse direction along the same path as the path along which thelight has traveled to the eye 111, and is split by the beam splitter 106such that a portion of the light is reflected toward the wavefrontsensor 115 and is used to measure the wavefront of the light.

In the present embodiment, a Shack-Hartmann sensor illustrated in FIGS.3C and 3D is used as the wavefront sensor 115.

Referring to FIG. 3C, the wavefront of a light ray 135 is measured. Thelight ray 135 is caused to pass through the microlens array 136, and iscollected on a focal plane 138 of a CCD sensor 137. FIG. 3D is asectional view of FIG. 3C taken along line IIID-IIID, which illustratesthe structure of microlenses 139 included in the microlens array 136.

The light ray 135 is collected on the CCD sensor 137 through themicrolenses 139. Therefore, the light ray 135 is collected at the samenumber of spots as the number of microlenses 139.

FIG. 3E illustrates the state in which the light ray 135 of which thewavefront is measured is collected on the CCD sensor 137. The light ray135 passes through the microlenses 139 and is collected at spots 140.

The wavefront of the incident light ray 135 is calculated from thepositions of the spots 140. For example, FIGS. 3F and 3G illustrate acase in which a wavefront having a spherical aberration is measured.

Here, it is assumed that the light ray 135 has a wavefront denoted by141. The light ray 135 is collected by the microlens array 136 atpositions corresponding to normal directions of local areas of thewavefront.

The state in which the light ray 135 is collected on the CCD sensor 137in this case is illustrated in FIG. 3G.

Since the light ray 135 has a spherical aberration, the spots 140 aredisplaced toward the center. The wavefront of the light ray 135 can bedetermined by calculating the positions of the spots 140.

The reflected and diffused light that has passed through the beamsplitter 106 is split by the beam splitter 104 such that a portionthereof is guided toward a photodetector 114 through a collimator 112and an optical fiber 113. The light is converted into electric signalsby the photodetector 114, and is reconstructed into a fundus image by animage processing unit 125.

In the first embodiment, an eyeball-movement detector 148 that detects amovement of the eye is provided as a position-variation detecting unitthat detects a position variation of a test object by detecting avariation with time in an obtained image.

The structure of the eyeball-movement detector 148 is not limited tothis. For example, the eyeball-movement detector 148 may directly detecta position variation of the eye.

The eyeball-movement detector 148 is connected to an adaptive opticscontroller 116, which is a control unit that performs feedback controlof the wavefront correction device 108 for correcting the aberrationcaused in the eye.

The adaptive optics controller 116 determines that the feedback controlof the wavefront correction device 108 is to be temporarily stopped onthe basis of information of the eyeball movement obtained as a result ofdetection (measurement) performed by the eyeball-movement detector 148.

As other examples of the structure for detecting the movement of theeye, eyeball-movement detectors using a method of detecting a line ofsight by irradiating the cornea with light (that is, a method ofdetecting a variation in the amount of light that returns from thecornea), a method of detecting the movement by measuring a specificposition on the eye using an interferometer, etc., may be provided.

When these structures are used, the optical system of the eyepiecesection is complex. However, it is not necessary to perform imageprocessing for detecting the position, and therefore the process speedcan be increased. In addition, the position detection accuracy can alsobe increased.

The wavefront sensor 115 is connected to the adaptive optics controller116. The wavefront sensor 115 transmits the wavefront of the receivedlight ray to the adaptive optics controller 116.

The wavefront correction device (deformable mirror) 108 is alsoconnected to the adaptive optics controller 116. The deformable mirror108 deforms into a shape specified by the adaptive optics controller116.

The adaptive optics controller 116 calculates a shape with which thewaveform can be corrected to a waveform without an aberration on thebasis of the waveform transmitted from the wavefront sensor 115, andcommands the deformable mirror 108 to deform into the calculated shape.

Feedback control is performed such that an optimum wavefront can becontinuously formed by repeating the processes of measuring thewavefront with the wavefront sensor 115, transmitting the measuredwavefront to the adaptive optics controller 116, and causing theadaptive optics controller 116 to command the deformable mirror 108 tocorrect the aberration.

In the present embodiment, if the eye temporarily moves during theimaging operation, the feedback control is temporarily stopped. Then,the feedback control is resumed when the eye returns to the originalposition. Accordingly, an image of the fundus can be obtained without atime loss.

More specifically, when the eyeball temporarily moves during the imagingoperation, the eyeball-movement detector 148 detects a positionvariation of the eyeball, and informs the adaptive optics controller 116that the position variation has occurred.

When the adaptive optics controller 116 is informed that the positionvariation has occurred (when a subject's eye moves out of apredetermined area, the adaptive optics controller 116 temporarily stopsthe feedback control while maintaining an aberration correction state atthe time when the eye has started moving. Then, when the eye returns tothe original position (when the eye moves into the predetermined area),the adaptive optics controller 116 resumes the feedback control from themaintained aberration correction state. The resuming of the feedbackcontrol means to make the correction on the basis of the amount ofaberration determined before the movement of the subject's eye to theoutside of the predetermined area. A determining unit that determinesthat the subject's eye has moved out of the predetermined area if theamount of aberration is lager than or equal to a predetermined value maybe provided. When the amount of aberration returns from a value afterthe movement of the subject's eye to a value before the movement of thesubject's eye, the determining unit can determine that the subject's eyehas moved into the predetermined area.

Next, an aberration correction process performed by the adaptive opticssystem according to the present embodiment will be described withreference to FIGS. 4A to 4C.

FIG. 4A illustrates the aberration correction effect obtained by anormal aberration correction function. The vertical axis shows themeasured amount of aberration and the horizontal axis shows the timerequired to correct the aberration by the feedback control.

As denoted by 142, the amount of aberration is about 3 μm at the timewhen the aberration correction process is started.

The feedback control of the correction device is performed on the basisof the measured aberration, so that the aberration is graduallycorrected. Accordingly, the aberration is substantially eliminated (thatis, the amount of aberration is reduced to an amount that is smallerthan or equal to a predetermined amount), as denoted by 143.

If the operation of obtaining a fundus image (for example, an OCT image)is performed at this time (at the time when the aberration issubstantially eliminated), a high-resolution image can be obtained.Since the aberration is corrected by the feedback control as describedabove, it takes a several seconds to reduce the amount of aberration toan amount at which a high-resolution image can be obtained.

While the feedback control is being performed to correct the aberration,the amount of aberration is still large and it is difficult to obtain ahigh-resolution image.

Next, a variation in aberration caused in the structure of the relatedart when the eye, which is a test object, moves will be described withreference to FIG. 4B.

When the eye moves, the measured aberration largely varies and thereforethe aberration correction system tries to correct the aberration thathas been varied.

Similar to the above-described case, the aberration is initially large,as denoted by 142, and is reduced by the aberration correction process,as denoted by 143. Then, if the eye moves, the light path to the eyechanges and therefore the aberration is greatly increased, as denoted by144.

In the aberration correction process, the feedback control is performedto reduce this increased aberration, and accordingly the aberration isgradually reduced.

However, since the imaging position is moved from the intended position,it is useless to obtain an image of the fundus at this time. Therefore,the imaging operation is not performed.

Then, if the eye returns to the original position, the light path to theeye also returns to the original light path, and accordingly theaberration is increased again, as denoted by 145.

The feedback control is performed to reduce this increased aberration,and it takes a long time to substantially eliminate the aberration, asdenoted by 146.

Since the eye is at the desired position at the time corresponding tothe point denoted by 145, it is desirable to resume the imagingoperation. However, a high-resolution image cannot be obtained for acertain time interval since the aberration is not yet eliminated.

An example of the aberration correction process according to the presentembodiment will be described with reference to FIG. 5.

First, the aberration correction process is started in step S101. Then,a reference position on the eye is set in step S102. The referenceposition is set to, for example, the position of a characteristicportion, such as a branching point of a blood vessel or an optic disc inthe fundus image.

In step S103, the aberration is measured by the wavefront sensor 115. Instep S104, the eyeball-movement detector 148 obtains eyeball positioninformation.

In step S105, the eyeball-movement detector 148 determines whether ornot the reference position of the eye has moved or whether or not theamount of movement of the reference position is small, and outputs theresult of the determination to the adaptive optics controller 116. If itis determined that the eye has not moved or the amount of movement ofthe eye is small, the adaptive optics controller 116 drives thecorrection device on the basis of the aberration information in stepS106.

If the eye has moved and is not at the desired position, the processproceeds to step S107 without performing steps S105 and S106. Therefore,the previous state of the correction device is maintained.

In step S107, it is determined whether or not a request for terminatingthe aberration correction process is issued. If the termination requestis not issued, the process returns to step S103. If the terminationrequest is issued, the process is terminated in step S108.

Another example of the aberration correction process will be describedwith reference to FIG. 6.

Similar to the above-described example, the aberration correctionprocess is started in step S101.

Then, a reference position on the eye is set in step S102. In step S103,the aberration is measured by the wavefront sensor 115. In step S104,the eyeball-movement detector 148 obtains the eyeball positioninformation.

In step S105, it is determined whether or not the eye has moved from thereference position. If the eye has not moved, the correction device isdriven on the basis of the aberration information in step S106.

If the eye has moved, the process proceeds to step S109 and determinesthe time elapsed from when the eye started moving.

If the elapsed time is longer than or equal to a certain time (if theeye is displaced for a time longer than or equal to a predeterminedtime), it is determined that it is necessary to perform the imagingoperation at the current position. Accordingly, the current position isset as the reference position of the eye in step S110.

Since the reference position is set to a new position, the aberrationcorrection process is performed on the basis of the measured aberrationfrom the next cycle.

Then, the process proceeds to step S107, where it is determined whetheror not a request for terminating the process is issued. If thetermination request is not issued, the process returns to step S103. Ifthe termination request is issued, the process is terminated in stepS108.

The manner in which the aberration correction state varies during theabove-described process according to the present embodiment will bedescribed with reference to FIG. 4C.

Similar to the above-described case, the aberration is initially large,as denoted by 142, and is reduced by the aberration correction process,as denoted by 143. Then, if the eye moves, the light path to the eyechanges and therefore the aberration is greatly increased, as denoted by144.

At this time, the eyeball-movement detector 148 detects the positionvariation of the eyeball and the adaptive optics controller 116maintains the state of the correction device. Since the state of thecorrection device does not change, the amount of aberration ismaintained at the amount at the point denoted by 144. However, this doesnot cause a problem since the imaging operation is not performed in thisstate.

The eye returns to the original position at the point denoted by 145.More specifically, the eyeball-movement detector 148 detects that theeye has returned to the original position (that is, that the eye is atthe predetermined imaging position), and the adaptive optics controller116 resumes the control of the correction device. At this time, thestate of the correction device is substantially the same as the state inwhich the initial aberration can be corrected. Therefore, the aberrationcan be substantially eliminated in a very short time, as denoted by 147.As a result, a high-resolution image of the fundus can be obtainedwithout a time loss.

Second Embodiment

An optical imaging apparatus and an optical imaging method in which anoptical image is obtained by an OCT apparatus including an adaptiveoptics system according to a second embodiment of the present inventionwill be described with reference to FIG. 2.

Referring to FIG. 2, in the present embodiment, a light source 101 is anSLD with a wavelength of 840 nm.

The light source 101 is not particularly limited as long as the lightsource 101 has a low coherence, and an SLD with a wavelength range of 30nm or more can be used.

Alternatively, an ultrashort pulse laser, such as a titanium-sapphirelaser, may be used as the light source 101.

Light emitted from the light source 101 travels through a single-modeoptical fiber 102 and is guided to a fiber coupler 117. The fibercoupler 117 divides a path of the light into a signal light path 118 anda reference light path 119.

A branching ratio of the fiber coupler 117 is 10:90, and 10% of thelight that reaches the fiber coupler 117 is caused to enter the signallight path 118.

The light that travels through the signal light path 118 is collimatedby a collimator 103, and is emitted as collimated light. The sectiondownstream of the collimator 103 is similar to that in the firstembodiment. More specifically, the light passes through the adaptiveoptics system and the scanning optical system, and is incident on theeye 111. Then, light reflected and diffused by the eye 111 travels alongthe same path as the path along which the light has traveled to the eye111, and is guided to the fiber coupler 117 through the signal lightpath (optical fiber) 118.

The reference light that travels through the reference light path 119 isemitted from a collimator 120, is reflected by a light-path-lengthchanging unit 121 including a stage and a mirror mounted thereon, andreturns to the fiber coupler 117.

The signal light and the reference light that reach the fiber coupler117 are combined together. The combined light is guided to aspectroscope 124 through an optical fiber 123. A tomographic image ofthe fundus is formed by an OCT image processor 125 a on the basis ofinterference light information obtained by the spectroscope 124.

The OCT image processor 125 a controls the light-path-length changingunit 121 so that an image at a desired depth can be obtained.

The OCT image processor 125 a is connected to an eyeball-movementdetector 148. The eyeball-movement detector 148 is capable of detectinga movement of the eye by detecting a variation with time in the obtainedimage.

The eyeball-movement detector 148 is connected to an adaptive opticscontroller 116. The adaptive optics controller 116 controls theaberration correction process using the information of the detectedeyeball movement.

According to the present embodiment, the optical imaging apparatusincludes the OCT apparatus, and the image obtained by the OCT imageprocessor 125 a is three-dimensional data. Therefore, athree-dimensional movement of the eyeball can be detected.

The adaptive optics controller 116 performs a control operation similarto that in the first embodiment, so that a high-resolution tomographicimage of the fundus can be obtained without a time loss even when theeye moves.

Third Embodiment

An optical imaging apparatus and an optical imaging method in which anoptical image is obtained by an SLO including an adaptive optics systemaccording to a third embodiment of the present invention will bedescribed with reference to FIG. 7.

The basic structure of the present embodiment is similar to that of thefirst embodiment. The present embodiment differs from the firstembodiment in that the eyeball-movement detector 148 is connected to theadaptive optics controller 116 but is not connected to the imageprocessing unit 125.

Referring to FIG. 7, light emitted from the light source 101 iscollimated by the collimator 103 and is guided to the eye 111 throughthe adaptive optics system and the eyepiece optical system, similar tothe first embodiment.

Light reflected and diffused by the eye 111 travels in the reversedirection along the same path as the path along which the light hastraveled to the eye 111, and is split by the beam splitter 106 such thata portion of the light is reflected toward the wavefront sensor 115 andis used to measure the wavefront of the light. The reflected anddiffused light that has passed through the beam splitter 106 is split bythe beam splitter 104 such that a portion thereof is reflected.

The reflected light is reflected and guided toward the photodetector 114through the collimator 112 and the optical fiber 113.

The light is converted into electric signals by the photodetector 114,and is reconstructed into a fundus image by the image processing unit125.

The wavefront sensor 115 is connected to the adaptive optics controller116. The wavefront sensor 115 transmits the wavefront of the receivedlight ray to the adaptive optics controller 116.

The deformable mirror 108 is also connected to the adaptive opticscontroller 116. The deformable mirror 108 deforms into a shape specifiedby the adaptive optics controller 116.

The adaptive optics controller 116 calculates a shape with which thewaveform can be corrected to a waveform without an aberration on thebasis of the waveform transmitted from the wavefront sensor 115, andcommands the deformable mirror 108 to deform into the calculated shape.

Feedback control is performed such that an optimum wavefront can becontinuously formed by repeating the processes of measuring thewavefront and commanding the deformable mirror to deform.

In the present embodiment, the eyeball-movement detector 148 detects themovement of the eyeball on the basis of the information obtained by thewavefront sensor 115, which is an aberration measuring unit.

As described above, when the eye moves by a large amount, the wavefrontmeasured by the wavefront sensor 115 greatly varies. Therefore, themovement of the eyeball can be detected by monitoring the variation inthe wavefront.

Similar to the first embodiment, when a movement of the eyeball isdetected, the correction device is not driven and the shape thereof ismaintained.

When the eye returns to the original position, it can be determined thatthe eyeball has returned to the original position since the wavefrontmeasured by the wavefront sensor 115 also returns to the previouslymeasured wavefront. When the eyeball returns to the original position,the adaptive optics controller 116 resumes the control of the correctiondevice. At this time, the state of the correction device issubstantially the same as the state in which the initial aberration canbe corrected. Therefore, the aberration can be substantially eliminatedin a very short time. As a result, a high-resolution image of the funduscan be obtained without a time loss.

As described above, according to the embodiments of the presentinvention, the optical imaging apparatuses including the SLO or the OCTapparatus may be structured as the imaging apparatuses for obtainingfundus images, and high-resolution images can be obtained even when theeye has an aberration.

Other Embodiments

Aspects of the present invention can also be realized by a computer of asystem or apparatus (or devices such as a CPU or MPU) that reads out andexecutes a program recorded on a memory device to perform the functionsof the above-described embodiment(s), and by a method, the steps ofwhich are performed by a computer of a system or apparatus by, forexample, reading out and executing a program recorded on a memory deviceto perform the functions of the above-described embodiment(s). For thispurpose, the program is provided to the computer for example via anetwork or from a recording medium of various types serving as thememory device (e.g., computer-readable medium).

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2009-262383 filed Nov. 17, 2009, which is hereby incorporated byreference herein in its entirety.

What is claimed is:
 1. An adaptive optics apparatus comprising: an aberration measuring unit that measures an aberration of returning light that returns from a subject's eye irradiated with light; an aberration correcting unit that corrects at least one of an aberration of light and an aberration of returning light that returns from the subject's eye irradiated with light on the basis of the measured aberration; a detecting unit that detects whether or not the subject's eye moves out of a predetermined area; and a control unit that controls the aberration correcting unit so as to hold a correction characteristic of the aberration correcting unit at a current correction characteristic, in a case where the detecting unit detects that the subject's eye moves out of a predetermined area, the current correction characteristic being a characteristic used for correction by the aberration correcting unit when movement of the subject's eye out of the predetermined area is detected.
 2. The adaptive optics apparatus according to claim 1, further comprising: a determining unit that determines that the subject's eye has moved out of the predetermined area in a case where an amount of the aberration is larger than or equal to a predetermined value.
 3. The adaptive optics apparatus according to claim 2, wherein the determining unit determines that the subject's eye has returned into the predetermined area in a case where the amount of the aberration returns from a value after the movement of the subject's eye to a value before the movement of the subject's eye.
 4. The adaptive optics apparatus according to claim 1, wherein the control unit performs feedback control of the aberration correcting unit on the basis of a measurement result obtained by the aberration measuring unit.
 5. The adaptive optics apparatus according to claim 4, wherein the feedback control includes measuring a first aberration using first light from a light source, correcting an aberration of light that returns from the subject's eye irradiated with the second light, the aberration being corrected by controlling the aberration correcting unit on the basis of the first aberration, measuring a second aberration using the corrected light, and correcting an aberration of third light from the light source by controlling the aberration correcting unit on the basis of the second aberration.
 6. The adaptive optics apparatus according to claim 4, wherein light used in the aberration measurement performed by the aberration measuring unit and light used to capture an image of the subject's eye are emitted from different light sources.
 7. The adaptive optics apparatus according to claim 4, wherein the aberration correcting unit corrects an aberration of light that returns from the subject's eye irradiated with the light, and wherein the aberration measuring unit measures an aberration of the light corrected by the aberration correcting unit.
 8. The adaptive optics apparatus according to claim 1, wherein the aberration is caused by an anterior segment of the subject's eye, and wherein the aberration correcting unit is disposed at a position where the aberration correcting unit is optically conjugate with the anterior segment of the subject's eye.
 9. An imaging apparatus, comprising: the adaptive optics apparatus according to claim 1, the adaptive optics apparatus being used to form an image of the subject's eye; and an image capturing unit that captures the image of the subject's eye on the basis of returning light that returns from the subject's eye irradiated with the light.
 10. The imaging apparatus according to claim 9, further comprising: a separating unit that separates light from a light source into light to be incident on the aberration correcting unit and reference light, wherein the image acquiring unit acquires a tomographic image of the subject's eye on the basis of interference light resulting from interference between the returning light that returns from the subject's eye irradiated with the light and the reference light.
 11. The imaging apparatus according to claim 9, further comprising: a detecting unit that detects a variation with time in the image, wherein the control unit maintains the correction characteristic of the aberration correcting means in accordance with a result of the detection by the detecting unit.
 12. The adaptive optics apparatus according to claim 1, further comprising: a detecting unit that detects either a position of the subject's eye or a line of sight of the subject's eye, wherein the control unit maintains the correction characteristic of the aberration correcting unit in accordance with a result of the detection by the detecting unit.
 13. The adaptive optics apparatus according to claim 1, wherein the control unit controls the aberration correcting unit so as to restart, in a case where the detecting unit detects that the subject's eye returns into the predetermined area, correcting the at least one of an aberration of the light and an aberration of the returning light from the correction characteristic.
 14. An adaptive optics method comprising: an aberration measuring step of measuring an aberration of returning light that returns from a subject's eye irradiated with light; an aberration correcting step of correcting at least one of an aberration of light and an aberration of returning light that returns from the subject's eye irradiated with light with an aberration correcting unit on the basis of the measured aberration; a step of detecting whether or not the subject's eye moves out of a predetermined area; and step of controlling the aberration correcting unit so as to hold a correction characteristic of the aberration correcting unit at a current correction characteristic, in a case where it is detected in the detecting step that the subject's eye moves out of a predetermined area, the current correction characteristic being that used for correction by the aberration correcting step when movement of the subject's eye out of the predetermined area is detected.
 15. The adaptive optics method according to claim 14, wherein the aberration correcting unit is controlled so as to restart, in a case where it is detected that the subject's eye returns into the predetermined area, correcting the at least one of an aberration of the light and an aberration of the returning light from the correction characteristic.
 16. An imaging apparatus comprising: an aberration measuring unit that measures an aberration of returning light that returns from an object irradiated with light; an aberration correcting unit that corrects at least one of an aberration of light and an aberration of returning light that returns from the object irradiated with light on the basis of the measured aberration; and a unit that starts an operation of acquiring an image of the object in a case where an amount of the measured aberration is smaller than or equal to a predetermined value.
 17. The imaging apparatus according to claim 16, wherein the unit starts the operation of acquiring a tomographic image of the object on the basis of interference light resulting from interference between returning light that returns from the object is irradiated with light and reference light.
 18. The imaging apparatus according to claim 16, wherein the unit starts the operation of acquiring an image of the object while the aberration correcting unit corrects the aberration, in a case where the amount of measured aberration is smaller than or equal to the predetermined value.
 19. The imaging apparatus according to claim 16, wherein the object is a subject's eye, and wherein the aberration correcting unit is arranged at a position optically conjugate with an anterior segment of the subject's eye.
 20. An adaptive optics apparatus comprising: an aberration measuring unit that measures an aberration of returning light that returns from a subject's eye irradiated with light; an aberration correcting unit that corrects at least one of an aberration of light and an aberration of returning light that returns from the subject's eye irradiated with light on the basis of the measured aberration; and a control unit that controls the aberration correcting unit so as to maintain, in a case where the subject's eye moves out of a predetermined area, a correction characteristic of the aberration correcting unit, and to restart, in a case where the subject's eye returns into the predetermined area, correcting the at least one of an aberration of the light and an aberration of the returning light from the correction characteristic.
 21. An adaptive optics method comprising: an aberration measuring step of measuring an aberration of returning light that returns from a subject's eye irradiated with light; an aberration correcting step of correcting at least one of an aberration of light and an aberration of returning light that returns from the subject's eye irradiated with light with an aberration correction unit on the basis of the measured aberration; and a control step of controlling the aberration correcting unit so as to maintain, in a case where the subject's eye moves out of a predetermined area, a correction characteristic of the aberration correcting unit, and to restart, in a case where the subject's eye returns into the predetermined area, correcting the at least one of an aberration of the light and an aberration of the returning light from the correction characteristic.
 22. A non-transitory computer-readable storage medium including a program stored therein for executing an adaptive optics method, the adaptive optics method comprising: an aberration measuring step of measuring an aberration of returning light that returns from a subject's eye irradiated with light; an aberration correcting step of correcting at least one of an aberration of light and an aberration of returning light that returns from the subject's eye irradiated with light with an aberration correction unit on the basis of the measured aberration; and a control step of controlling the aberration correcting unit so as to maintain, in a case where the subject's eye moves out of a predetermined area, a correction characteristic of the aberration correcting unit, and to restart, in a case where the subject's eye returns into the predetermined area, correcting the at least one of an aberration of the light and an aberration of the returning light from the correction characteristic.
 23. A non-transitory computer-readable storage medium including a program stored therein for executing an adaptive optics method, the adaptive optics method comprising: an aberration measuring step of measuring an aberration of returning light that returns from a subject's eye irradiated with light; an aberration correcting step of correcting at least one of an aberration of light and an aberration of returning light that returns from the subject's eye irradiated with light with an aberration correcting unit on the basis of the measured aberration; a step of detecting whether or not the subject's eye moves out of a predetermined area; and a step of controlling the aberration correcting unit so as to hold a correction characteristic of the aberration correcting unit at a current characteristic, in a case where it is detected in the detecting step that the subject's eye moves out of a predetermined area, the current correction characteristic being that used for correction in the aberration correcting step when movement of the subject's eye out of the predetermined area is detected.
 24. An imaging method comprising: an aberration measuring step of measuring an aberration of returning light that returns from an object irradiated with light; an aberration correcting step of correcting at least one of an aberration of light and an aberration of returning light that returns from the object irradiated with light on the basis of the measured aberration; and a step of starting an operation of acquiring an image of the object in a case where an amount of the measured aberration is smaller than or equal to a predetermined value.
 25. The imaging method according to claim 24, wherein the operation of acquiring a tomographic image of the object is started on the basis of interference light resulting from interference between returning light that returns from the object irradiated with light and reference light.
 26. The imaging method according to claim 24, wherein the operation of acquiring an image of the object is started while the aberration of corrected, in a case where the amount of measured aberration is smaller than or equal to the predetermined value.
 27. The imaging method according to claim 24, wherein the object is a subject's eye, and wherein the aberration correcting unit is arranged at a position optically conjugate with an anterior segment of the subject's eye.
 28. A non-transitory computer-readable storage medium including a program stored therein for executing an imaging method, the imaging method comprising: an aberration measuring step of measuring an aberration of returning light that returns from an object irradiated with light; an aberration correcting step of correcting at least one of an aberration of light and an aberration of returning light that returns from the object irradiated with light on the basis of the measured aberration; and an imaging-operation starting step of starting an operation of acquiring an image of the object in a case where an amount of the measured aberration is smaller than or equal to a predetermined value.
 29. An imaging apparatus comprising: an aberration measuring unit that measures an aberration of returning light that returns from an object irradiated with light; an aberration correcting unit that corrects at least one of an aberration of light and an aberration of returning light that returns from the object irradiated with light on the basis of the measured aberration; and a control unit that that starts, in a case where an amount of aberration measured by the aberration measuring unit is smaller than or equal to a threshold value, an operation of capturing an image of the object while performing feed back control of the aberration correcting unit on the basis of a measurement result obtained by the aberration measuring unit.
 30. The imaging apparatus according to claim 29, wherein the control unit starts the operation of capturing the image of the object by starting to construct the image of the object.
 31. The imaging apparatus according to claim 29, wherein the control unit starts the operation of capturing the image of the object by starting to acquire the image of the object.
 32. The imaging apparatus according to claim 29, further comprising: an acquiring unit that acquires a tomographic image of the object on the basis of interference light resulting from interference between returning light that returns from the object irradiated with measurement light and reference light corresponding to the measurement light, wherein the control unit controls the acquiring unit and starts the operation of capturing the image of the object while performing feedback control of the aberration correcting unit on the basis of a measurement result obtained by the aberration measuring unit.
 33. The imaging apparatus according to claim 29, wherein the object is a subject's eye, and wherein the aberration correcting unit is arranged at a position optically conjugate with an anterior segment of the subject's eye.
 34. An imaging apparatus comprising: a fundus imaging optical system that receives light reflected from a subject's eye and captures an image of a fundus of the subject's eye; a wavefront correcting device that is disposed in an optical path of the fundus imaging optical system, controls a wavefront of incident light and corrects a wavefront aberration of the subject's eye; a wavefront aberration detecting optical system that projects measurement light to the subject's eye and detect light reflected from the fundus with a wavefront sensor; and a control unit that performs feedback control of repeating detection of a wavefront aberration of the subject's eye on the basis of a detection signal from the wavefront sensor and control of the wavefront correcting device on the basis of a result of the detection, temporarily stops the feedback control on the basis of the detection signal from the wavefront sensor, and restarts the feedback control.
 35. The imaging apparatus according to claim 34, wherein the control unit temporarily stops the feedback control and restarts the feedback control on the basis of information on a wavefront of reflected light detected by the wavefront sensor.
 36. The imaging apparatus according to claim 34, wherein the control unit temporarily stops the feedback control and restarts the feedback control on the basis of a change in the wavefront of reflected light detected by the wavefront sensor.
 37. The imaging apparatus according to claim 34, further comprising: a detecting unit that detects movement information about the subject's eye on the basis of a detection signal from the wavefront sensor, wherein the control unit temporarily stops the feedback control in a case where the movement information detected by the detecting unit is out of a predetermined range, and restarts the feedback control in a case where the movement information returns into the predetermined range.
 38. The imaging apparatus according to claim 37, wherein the control unit reflects, on the wavefront correcting device, information on controlling the wavefront correcting device when the movement information is within the predetermined range, in a case where the movement information returns into the predetermined range.
 39. A method of controlling an imaging apparatus including a wavefront correcting device that is disposed in an optical path of a fundus imaging optical system that receives light reflected from a subject's eye and captures an image of a fundus of the subject's eye, controls a wavefront of incident light and corrects a wavefront aberration of the subject's eye, and a wavefront aberration detecting optical system that projects measurement light to the subject's eye and detect light reflected from the fundus with a wavefront sensor, the method comprising: performing feedback control of repeating detection of a wavefront aberration of the subject's eye on the basis of a detection signal from the wavefront sensor and control of the wavefront correcting device on the basis of a result of the detection; and temporarily stopping the feedback control on the basis of the detection signal from the wavefront sensor, and restarting the feedback control.
 40. A non-transitory computer-readable storage medium including a program stored therein for executing a method of controlling an imaging apparatus including a wavefront correcting device that is disposed in an optical path of a fundus imaging optical system that receives light reflected from a subject's eye and captures an image of a fundus of the subject's eye, controls a wavefront of incident light and corrects a wavefront aberration of the subject's eye, and a wavefront aberration detecting optical system that projects measurement light to the subject's eye and detect light reflected from the fundus with a wavefront sensor, the method comprising: performing feedback control of repeating detection of a wavefront aberration of the subject's eye on the basis of a detection signal from the wavefront sensor and control of the wavefront correcting device on the basis of a result of the detection; and temporarily stopping the feedback control on the basis of the detection signal from the wavefront sensor, and restarting the feedback control.
 41. A method of controlling an imaging apparatus including an aberration measuring unit that measures an aberration of returning light that returns from an object irradiated with light and an aberration correcting unit that corrects at least one of an aberration of light and an aberration of returning light that returns from the object irradiated with light on the basis of the measured aberration, the method comprising: starting, in a case where an amount of aberration measured by the aberration measuring unit is smaller than or equal to a threshold value, an operation of capturing an image of the object while performing feedback control of the aberration correcting unit on the basis of a measurement result obtained by the aberration measuring unit.
 42. The method according to claim 41, wherein the object is a subject's eye, and wherein the aberration correcting unit is arranged at a position optically conjugate with an anterior segment of the subject's eye.
 43. A non-transitory computer-readable storage medium including a program stored therein for executing a method of controlling an imaging apparatus including an aberration measuring unit that measures an aberration of returning light that returns from an object irradiated with light and an aberration correcting unit that corrects at least one of an aberration of light and an aberration of returning light that returns from the object irradiated with light on the basis of the measured aberration, the method comprising: starting, in a case where an amount of aberration measured by the aberration measuring unit is smaller than or equal to a threshold value, an operation of capturing an image of the object while performing feedback control of the aberration correcting unit on the basis of a measurement result obtained by the aberration measuring unit. 